The IJN was certainly involved in the Sino-Japanese War, despite claims advanced during the postwar that it was the more "peaceful" of the two services. The IJN used the outbreak of hostilities as a laboratory of sorts to work out various aspects of its doctrine such as strategic air bombardment, carrier attacks, and amphibious landings, all of which it would later put to use in its long-cherished goal of a Nanshin (southern drive). The war helped to hone the IJN's air arm, which included a sizable land-based contingent, as the IJN was responsible for air operations over central and southern China. G3Ms operated from Taiwan and Kyushu against mainland targets and the IJN's carriers raided along the coasts and Yangtze river valley.

The early stages of the war exposed the strengths and shortcomings of IJN equipment, Although the main frontline IJN fighter, the A5M, was more than adequate for operations in China, the single-seat attack aircraft showed their age in operations against the KMT's American- and Soviet-built fighters. This gave the IJN an added incentive to modernize its air arm with new equipment and replace its stable of frontline aircraft. The war also exposed the problems in elements of IJN air doctrine. Some of these lessons, such as the vulnerability of unescorted bombers or the inefficacy of escort gunship bombers, the IJN learned before other air arms over China and they put these lessons to good use in 1941/42. The IJN was one of the few air arms that entered into the Second World War prepared to assign fighters as bomber escorts. Other problems that the China War exposed went unresolved. The IJA's relative disinterest in long-range air operations meant that the IJN frequently had the thankless task of undertaking long-range aerial offensives after the Wuhan campaign. These raids, some of which struck deep into the Chinese hinterland as far as the western border with Inner Mongolia, showed the problems of navigation and bombing accuracy and neither problems were resolved. The IJN's fighter arm also imbibed some of the wrong lessons from the China War with an overemphasis upon maneuverability and acrobatics to win air superiority. Such tactics worked well against numerically outnumbered KMT air force, but it was not a tactic that was viable against a foe like the US.

As for the Republic of China Navy (ROCN) , it really did not pose much of a threat to the IJN's operations. The ROCN was numerically outnumbered by the IJN and was able to be swiftly bottled up in its harbors. In September 1937, IJN carriers were able to sink the two largest ROCN ships, the light cruisers Ping Hai and Ning Hai as part of its larger operations against Shanghai. IJN naval superiority allowed it to range throughout Chinese waters to blockade Chinese shipping, leaving the KMT reliant upon overland supply routes. But such naval superiority did not always translate into immediate successes. The amphibious landings the IJN conducted in the initial stages of the war were haphazardly organized and had high losses. This poor performance of IJN marines in these early campaigns forced the IJN to reexamine its amphibious warfare doctrine, and underscored the need for specialist troops for this task, thus justifying the formation of the Special Naval Landing Forces (SNLF) and greater coordination between planning and execution. This allowed the IJN to carry out a series of landings in 1938-39 in the South China Sea, most notably around Hainan Island in February 1939. The seizure of southern Chinese territory allowed the Japanese to have an advanced base to further project power in southeast Asia. But like its air lessons, experience with amphibious operations proved to be a mixed blessing. The IJN became proficient at unopposed landings, which allowed them to swiftly build a bridgehead, but the relative weakness of KMT troops meant the IJN went into the Pacific War with very little experience against stiffer opposition. Thus IJN doctrine for landing fire-support remained underdeveloped and a determined resistance could throw IJN landings in disarray, as it did during the first Wake Island invasion attempt.

The sources for the IJN's war in China are somewhat few and far between. David Evans and Mark Peattie's Kaigun and Peattie's Sunburst have good coverage if IJN operations and how they fit into the bigger picture. Robert D. Hackett, Sander Kingsepp, and Antony Tully have an excellent web account of the IJN and the Second Sino-Japanese War, Rising Storm- The Imperial Japanese Navy and China, but unfortunately, their bibliography is a dead link.